In a recent study on the minimum requirement leucine we observed a peculiar pattern in leucine oxidation after three equal "bulk meals" and an apparent positive balance due to a 24h leucine oxidation 22% lower than the intake. Therefore, we need to investigate whether and, if that is the case, to what extent our tracer model underestimates leucine oxidation in experimental conditions involving bulk meals. We also need to understand if the lower oxidation observed at lunch is due to an increased splanchnic uptake or simply to a larger portion of "first pass" uptake of leucine which undergoes to oxidative metabolism. To achieve these goals we will perform in each volunteer a series of three 24h tracer infusionsby administering simultaneously D3 and 13C leucine orally and I.V.